Military garrisons used bugle megaphones to amplify the sound of the bugle. Usually, these pedestals were located near the main flagpole or at garrison headquarters. The bugler could use the megaphone in any direction and the sound would carry over a broader area when mounted on a post swivel to use in a garrison environment.
Megaphones are portable or hand-held horns that amplify sound and direct it in a particular direction. Holding the megaphone up to the face and speaking into it introduces sound into the narrow end, emitting sound waves out the wide end. The megaphone distorts the sound somewhat because its frequency response is more significant at higher sound frequencies. Furthermore, it serves to direct sound waves in the direction of the horn. By increasing the acoustic impedance seen by the vocal cords, a megaphone produces more sound power by matching the impedance of the vocal cords to the air.